Tuesday, July 8, 2014

Fall webworm colonies becoming obvious

    Driving along the highway, I've started to notice numerous colonies of the Fall Webworm. Webworms create a white web around their colony of 30 to 100 caterpillars (photo at right). The web serves as protection against both predators and parasites. Each evening the caterpillars work to extend the web further out into the canopy to capture fresh green leaves to feed on. The webs we are seeing now represent the first summer generation of the fall webworm. A second generation will appear in late August to early September.

   If you look closely inside the web, you will see an army of yellow to rust-orange caterpillars feeding of pecan leaves (photo at left). At maturity these caterpillars will grow to 1.5 inches long and be covered with long white hairs. Eventually, larvae leave their protective web and drop to the ground. The caterpillars will then crawl into ground-cover litter and pupate. A white moth will emerge from the pupal case and fly up into the trees to initiate a second summer generation.
   Many folks believe that they need to penetrate the web with an insecticidal spray to control this pest. Since the caterpillars are continuously expanding their web in a quest for more green leaves, applying an insecticide on the foliage surrounding the web will effectively control this pest.
    In commercial pecan groves, there should be more than 5 colonies per acre to justify an orchard wide insecticide treatment. This spring, I have seen very few webworm colonies in pecan groves that were sprayed for pecan nut casebearer. It seems that the residual action of the earlier applied insecticide treatment has kept early-hatch webworms in check.